DE3108924C2 - Method and device for the chromatographic separation and quantitative analysis of ions - Google Patents

Abstract

Process and device for the chromatographic separation and quantitative analysis of ions with the same charge in a sample, e.g. of cations or anions. To analyze the inorganic anions, the sample and an eluent are passed onto a column with a hydrophobic, porous chromatographic separation medium (organic resin or bonded phase) with a large surface area and without permanently adhering ion exchange sites. The eluant (a polar mobile liquid) comprises an organic cation which is reversibly bound to the resin and creates ion exchange sites which differentially delay the anions for chromatographic separation. The eluant also includes a developing reagent of the same charge as the ion to be analyzed. The eluant including the separated anions is then passed through an ion exchange resin, which excludes the passage of the counterion and its co-ions in ionic form, and then through a conductivity cell for quantitative detection. Inorganic cations can be detected in a similar way. The system can also be used for the analysis of largely organic cations or anions (e.g. of surface-active substances). In this case, the organic ion of interest is already strongly attracted by the porous chromatographic separation medium and thus the counterion can be an inorganic ion.

Description

2. The method according to claim 1, characterized in that the polar mobile liquid phase a substantially nonionic, organic polar compound in an amount with which the Delay time of the ions in the bed can be controlled.

3. The method according to claim 1 or 2, characterized in that the polar mobile liquid phase is a development reagent; -, i including one contains inorganic development ions of the same charge as the ions in a mixture with the the delay time of the ions in the bed can be controlled, the development ion and its co-ion are excluded from passage through the second column in ionic form.

4. The method according to any one of claims 1 to 3, characterized in that the chromatographic resin has a surface area of at least 100 ^mJ / g.

5. The method according to any one of claims 1 to 4, characterized in that the chromatographic Resin has a solubility parameter ranging between about 7.5 and 15.0.

6. The method according to any one of claims 1 to 5, characterized in that the Co ion of the counterion is a hydroxide, borate or carbonate.

7. The method according to any one of claims 1 to 6, characterized in that the second column is a Cation exchange column is in the hydrogen form.

8. The method according to any one of claims 1 to 7, characterized in that the anions are inorganic Anions are used.

9. The method according to any one of claims 1 to 8, characterized in that an alkylammonium ion as the counterion is used.

10. The method according to any one of claims 1 to 5, characterized in that as a co-ion of the counterion Hydrogen is used.

11. The method according to claim 10, characterized in that that a cation exchange column in the hydroxide form is used as the second column.

12. The method according to any one of claims 1 to 11, characterized in that the chromatographic bed consists of an organic resin.

13. The method according to any one of claims 1 to 12, characterized in that a chromatographic Bed is used which contains hydrocarbon chains attached to a substrate

14. The method according to claim 13, characterized in that the substrate contains silicon dioxide.

15. Device for chromatographic separation and quantitative analysis of ions in one polar mobile liquid phase, containing a common counterion for the ions, characterized by

a) a first column with a porous, hydrophobic chromatographic bed without permanent adherent ion exchange sites, the bed containing hydrocarbon chains which are present in the Are capable of reversible adsorption bonds with organic components in the polar mobile To form liquid phase,

b) a second column with an ion exchange resin bed and

c) a device for measuring conductivity and a reading device connected to it, wherein the conductivity measuring device comprises at least one flow conductivity cell.

16. Device according to claim 15, characterized in that that the substrate in the first column contains silicon dioxide

17. Device according to claim 15, characterized in that the chromatographic bed consists of an organic resin

The invention relates to the quantitative analysis of anions or cations in a single system (such as apparent from the preamble of claim 15). the Reverse phase chromatography (RPLC) is widely used as a type of separation in high performance liquid chromatography (HPLC). In the RPLC, the mobile phase is more polar than the stationary phase while in conventional chromatography, where the predevelopment of the RPLC was carried out, the Conditions are reversed. Chemically bound hydrocarbon chains adhering to silicon dioxide substrates (Alkyl radicals) are a common form of the stationary phase. The nature of the formation of such stationary Phases and suitable techniques for performing the RPLC are e.g. B. by N. H. C. Cooke and K. Olsen. At the. Lab., 45 (August 1979). Reverse phase ion pair chromatography (Reversed Phase Ion Pair Chromatography) is popular enough won. In this technique, a salt is added to the mobile phase to improve the chromatographic Properties to improve. While opinions differ on the theory of separation, the experimental techniques described therein are generally applied, in particular the sample passed into an aqueous polar mobile phase, which is usually a lower alcohol, Contains acetonitrile or other water-miscible organic solvent, along with a Counterion, which is typically the tetrabutylammonium ion (TBA) when analyzing anions. According to one theory, hydrophobic ion pairs are

forms, which are relatively non-polar and are thus delayed differently by the column. According to another theory, the counterion, for example TBA, is absorbed on the surface and forms a reversible ion exchange site on the stationary phase. This technique is mainly used for the chromatographic separation and analysis of organic acids and bases. In general, the usual HPLC detectors are used, e.g. B. Ultraviolet, fluorescence, and refractive index (Ri) detectors. However, these typical detection techniques are unsuitable for the analysis of the inorganic substances separated by RPLC. In addition, they are _{relatively insensitive to non-chromophoric organic molecules with low pK a} or pK b, such as surfactants.

In US-PS 40 42 327 a reverse phase ion pair chromatography is using a bonded phase fill. The ones to be analyzed Species are generally limited to organic compounds The filling is at high and low pH levels unstable and can therefore only be used for the analysis of inorganic anions Lew. Cations use.

In a recent publication by F. F. Cantwell and S. Puoh, Anal. Chenu 51, No. 5 (May 1977), p. 623, the use of a non-ionic macroporous resin (a copolymer of styrene and divinylbenzene, which is sold under the trademark Amberlite XAD-2) as the stationary phase for the RPLC described. A significant advantage of using this resin is its stability at extremes pH ranges in contrast to a stationary phase based on silicon dioxide. Everybody wise them conventional determination techniques as described above suffer from the same disadvantages.

Another chromatographic system, which is referred to as ion chromatography, was used for the quantitative determination of organic and / or inorganic anions and / or cations in aqueous sample solutions. According to this technique, the chromatographic separation is carried out on one or more columns with low capacity ion exchange resin. The eluant is then passed through a barrier column with a high capacity ion exchange resin, which converts the eluant from a conductive form to a non-conductive form and thus reduces the background conductivity of the chromalographic system. The ions to be analyzed are eluted from the barrier column and form highly conductive ions, which are passed through a conductivity cell and are quantitatively determined by their conductivity. This technique is well suited for ions which are eluted from the barrier column in a form which has a dissociation constant with a value of more than 10 " ^Ί . Molecules with lower dissociation constants cannot be determined due to the conductivity at chromatographic concentration ranges.

One limitation of ion chromatography is that the separating resin a conventional permanent must be resin containing ion exchange sites. This basically sets both the ion exchange capacity and the selectivity of the separating column is fixed, since the ion exchange groups are chemically attached to the substrate resin are bound. Somii requires at a given Column and a given resin a modification of the chromatographic separation a chemical Modification of the resin, such as changing the ion exchange groups by using a different one Resin type. This is a time consuming and expensive process. The capacity of the release resin must be small, so that eluents with relatively low ionic strength can be used to increase the service life to maximize the barrier pillar. The separation of highly ionized ions according to this technique is for example in US-PS 39 20 397 described.

ίο The object of the invention is to find the best properties the aforementioned known reverse phase ion pair chromatography and ion chromatography. This object is achieved as can be seen from the preceding claims

In particular, it is an object of the invention to provide an ion chromatography technique according to which the chromatographic selectivity and the chromatographic capacity merely by changes can be varied in the composition of the eluant and the concentration.

This superior chromatographic separation technology should be combined with the superior: Errattlungs-System of ion chromatography, whereby the highly selective and sensitive determination and quantitative determination of ions with low pK _a - or pKt, -values is facilitated. Optimization should also be facilitated the ion separation over a large selectivity range can be created by such changes in the eluant without rapid consumption of the barrier column.

Finally, there should be provided a technique for separating and detecting large organic ions which are difficult to perform with conventional ion chromatography and for which the detection limits of conventional reverse phase ion pair chromatography using ultraviolet or refractive index detectors are not suitable. In particular, it should be possible to use a porous, hydrophobic chromatographic resin, which is stable to extremely high pH levels and is therefore suitable for the extended chromatographic operation of inorganic anions without destruction, as the stationary phase.
A possible interpretation of the events follows. Thereafter, instead of the counterion of the exchange site forming compound forming reversibly absorbed ion exchange moieties, the counterion and the ions form reversible ion pairs which are reversibly absorbed on the chromatographic bed and cause different delay and chromatographic resolution. The separated ions are then passed through the barrier column and the conductivity cell. This theory best explains the separation of organism molecules with long chains, such as surface-active substances, which form the primary adsorptive bonds of the ion pairs. Indeed, inorganic counterions are preferred in the analysis of such organic ions to allow desorption from the column in a reasonable time.

Fig. 1 shows a schematic representation of a simplified device according to the invention;

FIGS. 2 to 6 show chromatograms showing the Represent separation of different ions according to the technique according to the invention. "

The system according to the invention is very versatile and can be used to determine a large number of strong and / or weak organic and / or inorganic

Ions are used as long as these ions to be determined are only of a cationic or anionic nature are. Such ions are usually associated with counterions, but according to the invention Method only ions of a common charge can be determined. Suitable samples include Surface water, including salt water and other liquids, such as industrial chemical wastewater streams, Body fluids such as serum and urine, beverages such as fruit juices and wines, and drinking water. Covalent molecular compounds, such as amines, are converted into an ionic form by the formation of acid salts are transferable, can also be analyzed according to the invention. The term "ions" used here includes Ions and parts of molecules which are ionizable under the conditions of the present process are.

F i g. 1 shows a simplified device for carrying out the method according to the invention. The sample is expediently introduced into the system by means of a syringe (not shown) at the sample injection valve 10 brought in. The sample is conveyed through the system from the storage container by means of an eluant 11 by a pump 12, which is then inserted into the chromatographic separation column 13 of a further below the type described. The eluant from column 13 passes through the barrier column 14, in which ions with the ions to be analyzed of opposite charge, essentially from the passage in ionic form excluded are. Typically this is accomplished by withdrawing these ions. The eluent then flows through a liquid line to the conductivity cell 15. The electrical signal that is sent to the cell 15, in which the fluctuation of the ionic concentration generates an electrical signal, which is proportional to the amount of ionic material measured by a conductivity meter 16 is registered, the registration device 17 which provides a visual reading for the signal from the conductivity cell 15. After going through the conductivity cell, the liquid is discarded.

The nature of the separation in column 13 can be explained by two different theoretical mechanisms which are referred to here as "ion pair theory" and "theory of reversible ion exchange". Regardless of the prevailing theory, the system uses a mobile polar phase, which in its character is more polar than the stationary phase which carries a counterion, which with the to be determined Ions interacts. This type of system is commonly referred to as a "reverse phase process." In the early stages of the work with reversed phases, the ion-pair theory (as described in the previously mentioned article described by Cooke and Olsen) is considered applicable, while some more recent publications give preference to the other theory, which is explained in more detail below will. The invention can be explained according to either or both theories and the combination the use of the reverse phase method for chromatographic separation together with the Ion chromatography technique for quantitative determination the separated ions forms an essential aspect of the invention.

The process is initially in agreement with the separation theory via reversible ion exchange described. For simplicity of description, inorganic anions are first mentioned in the sample which are to be determined separately and quantitatively in the system. The eluent in the Reservoir 11, which the mobile polar phase for forms the sample contains an ion exchange moiety forming compound. This compound includes a counterion with a charge opposite to the ions to be determined and a Co-ion one which is identical to the ions Charge. (In the following, the term “counterion” refers to the last-mentioned counterion on its own and the term "co-ion" alone indicates the co-ion of the counterion.) A porous hydrophobic chromatographic Bed with essentially no permanently adhered ion exchange sites is in the Separating column 13 included. This is to be distinguished from a conventional ion exchange resin, in which the ion exchange sites adhere permanently to the resin substrate by covalent bonding.

According to the theory of reversible ion exchange, the counterion is of a type that has reversible adsorption bonds forms in situ in the chromatographic bed, thus creating ion exchange sites therein. In this way, the ions to be separated are delayed differently by the ion exchange points formed in this way and are separated from this bed by chromatography in the eluent. The inorganic Anions to which the present technique can be applied include essentially all Types from the species weakly to strongly retained on the chromatographic bed. For example the following anions can be separated: fluoride, chloride, nitrite, nitrate, chlorate, perchlorate, bromide, Bromate, iodide, iodate, sulfate, thiosulfate, persulfate, pyrosulfate, Phosphate, pyrophosphate, azide. Cyanide, ferricyanide and thiocyanate.

Prior to the time of the invention, it was not believed that inorganic anions or cations were among Applying one of the two theoretical mechanisms described above can be separated can.

A variety of stationary separation phases for reversed phase chromatography, such as the one in the article type mentioned by Cooke and Olsen can be used. An effective type of a chromatographic Beds that can be used for the stationary phase include those bound to a substrate Hydrocarbon chains. These chains are typically 8 to 18 carbon atoms in length. Such chemically bonded alkyl phases are usually produced by reacting a surface silicon dioxide silanol made with organochlorosilanes The type of chain can be varied depending on of the ions of interest. Appropriately, the bed provides uniform surfaces with organic Chains so that the counterion absorbs in a uniform repeatable manner on the surface will.

A typical filling of phase-bound porous silica gel consists of silicon dioxide, which is mixed with a organic material has been converted to an 18 carbon chain of an aliphatic To wear the rest. Such a pack is available from Waters Associates, Ine, under the trade name Distributed Bondapak Cis. Other suitable Resins are supplied by Altex Corporation and Merck & Co, Ine.

A particularly effective stationary phase is a non-ionic, porous, hydrophobic, organic Resin with essentially no ion exchange sites.

One such resin is a copolymer of styrene and divinylbenzene available under the trademark Amberlite XAD-2 and having a surface area of about 300 m ² / g. Such resins are stable at extreme pH values, ie 1 to 14, compared to the phase-bonded fillings which have been described above and are less stable at extreme pH values.

Conventional nonionic, hydrophobic, porous, organic resins can be used according to the invention for separation if they have a sufficiently large surface area and have sufficient hydrophobic properties. A suitable minimum surface area is values from about 10 to 100 mVg up to a maximum value of 1000 mVg or more, with a preferred range from about a minimum value from 200 to 300 m ² / g up to 600 m ² / g. Typical pore sizes are in the range from 30 Å to 100 Å and 200 Å or higher. Such porous resins are generally produced using porogens or so-called precipitants. Suitable resins and processes for their preparation are described in US Pat. No. 3,531,463 and US Pat. No. 3,549,563. The method for determining the surface area is mercury porosimetry, which is described in the article "Advanced Experimental Techniques in Powder Metallurgy", Volume 5, Plenum Press (1970).

An important feature of the chromatographic bed is that as a result of its large size Above the surface area there is a correspondingly high capacity to form reversible ion exchange sites with the counterions. This high capacity has the The advantage is that the amount of filler material required is minimized. It is known that the adsorption capacity of a chromatographic fill is proportional to the surface area of the fill.

Another feature of the Füiiung is that it is sufficiently hydrophobic that the organic Counterion is adsorbed on the surface of the resin and is thereby recorded by chromatography. One suitable hydrophobic starch is comparable to a copolymer of styrene and divinylbenzene. In a different In nature, the preferred fillings are crosslinked resins with solubility parameters

(expressed in the units

1 / calories λ
V cm ^j J

from at least 7.5 up to 15.0 and typically from about 9.

With regard to anionic analysis, suitable ion exchange sites are Forming compounds: tetrabutylammonium hydroxide, mono-, di-, tri- and tetra-alkylammonium hydroxide. The counterions for the analysis of inorganic anions must be the opposite of the anions Carry charge and be of a type which is capable of reversible adsorptive bonds with the to form chromatographic bed. This means that such counterions comprise organic chains must, especially alkyl chains, of sufficient length for easy adsorption on the column, like it is too difficult to remove in a reasonable time. Another parameter of the ion exchange sites forming compound of the invention is that it must have the property essentially to be excluded from the flow through the barrier column 14 in ionic form. As explained below is, in the case of an anion to be investigated, the barrier column comprises a cation exchange resin and the counterion, which is such that it can be removed or stripped through the column 14. The colon's Counterion passes through the column, but in an essentially non-ionized form. Such Co ions include the carbonate, borate and hydroxide ions, all of which are weakly ionized acids or water in the barrier column form. However, in those cases where silicon dioxide

ίο forms the chromatographic bed, the hydroxide ion has limited utility due to the Dissolution of silicon dioxide at higher pH levels. The extent of absorption of the counterion is determined the column capacity, which is tailored to the desired retention time for a specific sample can be, by controlling the amount of organic polar liquid. For example, was experimental found that the degree of absorption of tetrabutylammonium hydroxide (TBAH) increases considerably, when the amount of organic liquid (for example acetonitrile) decreases. The size of the TBAH adsorption is relatively low (e.g. 0.023 meq./ml for 100% water as eluant). Compared with the exchange capacity of an ion exchange resin (e.g. 0.5 to 1.5 meq./ml). Thus the capacity of a reversed phase column is in limited of this type. Typically the capacity of a system containing 0.004 molar TBAH is up limited to about 2 to 4 micrograms of each ionic component per injection.

For the analysis of cations, the compound forming ion exchange sites must be of a type which is formed from a counter ion and a Co ion, which have properties such that they essentially excluded from passage through the anion exchange resin barrier column in hydroxide form are. Suitable counter-ions for this purpose include: lauryl sulfuric acid, Ci —C »-Alky! Sulfuric acid or alkyl sulfonic acid. The counter-ions are retained in the column, while the co-ion, hydrogen, is removed from the barrier column 14 in the form of water molecules.

The mobile phase comprises the sample and the counterion in a polar aqueous liquid. The polar The nature of the liquid aids the ionization and dissolution of the ionic components in the system the mobile phase.

Another preferred component of the mobile phase is a substantially non-ionic, organic, polar compound in an amount that serves to selectively reduce the delay time of the ions in the bed in in a controlled manner. This organic, polar compound is essentially non-ionic, so that it does not interfere with the ionic conductivity measurement. For one, the organic compound serves as a mobile one attractive force for the counter ions and thus for the ions of interest in order to establish an equilibrium, which removes these ions from the chromatographic column and selectively transfers them to the mobile phase transferred for separation On the other hand, the organic, polar liquid occurs with the organic counterion in competition for the accessible adsorption binding sites on the stationary phase to cause a decrease in its capacity. In this case A higher concentration of such an organic, polar compound reduces the delay time Suitable organic, polar compounds include lower alcohols such as methanol and ethanol,

Acetonitrile, or any water-miscible organic solvent.

The concentration and nature of the organic, polar compound can be remarkable in one Extents can be varied to modify the desired delay time, depending on the one to be used analyzing isnen. Appropriate concentrations of a such organic polar liquid can be varied from 0 to 100%, with the higher concentrations can be used with more firmly retained counterions. Solubility problems can occur at the upper limit for the ions of interest exist, and so it is preferred to keep water in the mobile Phase to use.

Another component of the mobile liquid phase is a developing agent, which is an inorganic one Development ion having the same charge as the ions. This ion is present in abundance to selectively see the residence time of the ions in the chromatograph Decrease gene. The Entv / ick'.up.gsion and its co-ion (hereinafter referred to as "co-ion of the development ion") must be of a type that is essentially excluded from passage through the locking pillar 14. Suitable development ions include borate and carbonate ions. These two ions are converted into hydrogen ion form by a barrier column converted to their corresponding acids, which are only weakly ionized and therefore do not create an overlay that would significantly interfere with the conductivity cell. Similarly, the co-ion becomes of the development ion is either withdrawn through the column or is in its hydrogen ion form, which is the desired shape of the ions for the determination in the conductivity cell.

The same principles are used for the analytical determination of cations. In this case include suitable development center! a variety of mineral acids, their anions through the barrier column 14 can be withdrawn to form water.

The development agent has a similar function as development center! in conventional ion exchange separations, in which the ion exchange sites permanently adhere to the resin substrate. That means that the developing agents exert an equilibrium force and thereby shift the ions of interest out of the stationary phase, thereby reducing the delay time will.

The pH level of the elution solution is another parameter which affects the chromatographic separation Influence and can be tailored to the ions of interest. The present porous Resin is stable at extreme pH levels.

As with the polar organic liquid, the type and concentration of the developing agent can be varied are dependent on the desired delay time. However, at high concentrations the Barrier column can be exhausted quickly. Even though the developing agent is generally used to modify The selectivity and capacity of the separating bed is more suitable than the polar organic liquid, so must its The type and concentration must be carefully considered to avoid excessive depletion of the barrier resin.

From the foregoing it can be seen that one of the significant advantages of the system is its Ability is to vary the developing agent, the other organic liquid and the counter ion to achieve the Adapt system separation to the specific ionic species to be analyzed.

The blocking column 14 is the stripping column in its function 11 in Fig. I of US-PS 39 20 297 analog. The rules of operation of this column, their detailed description and relationships and functional features with respect to the separation column are described there, whereupon this is hereby incorporated by reference. In the present system, the column 14 has a relatively high specificity Ion exchange capacity. This is because the main function of this barrier pillar is prevention the passage of the developing agent and the ion exchange sites forming compound is in strongly ionized form while allowing the passage of ions, which has been separated in the separation column 13, allows without significant interruption. Suitable ion exchange resins for the analysis of anions are polystyrene or modified, with divinyibenzene, which Carries core groups, crosslinked polystyrene, with the divinylhenzene creates reactive exchange points. The strong cation exchange resins typically include sulfonic acid or sulfonate residues containing aromatic nuclei along the polymer chains, while the weak ion exchange resins, carboxylate residues

gene.

The strong base anion exchange resins carry core chloromethyl radicals which have been quaternized. The weak base exchange resins have primary, secondary or tertiary amine residues on the aromatic core.

The nature of the resin in the barrier pillar 14 is determined by the compound forming the ion exchange parts and the developing agents to be suppressed are determined. A suitable resin for anion analysis is a highly crosslinked one Polystyrene with sulfonic acid residues in the hydrogen ion form. The high level of networking ensures that the ion exchange effects outweigh the chromatographic penetration into the resin. The counterion and the co-ion of the development ion are modified by ion exchange in the barrier column and form products which elute from the column in substantially non-ionized molecular form and which therefore do not override the determination in the conductivity cell.

The outflow from the barrier column 14 is passed through the conductivity cell 15 and subsequently to the Waste products. The electrical signal from the conductivity cell is sent to the conductivity meter 16, and the output is passed to the register 17.

The separation mechanism is changed depending on the nature of the ions to be analyzed If the sample of ions becomes more hydrophobic (organic) in nature, it is assumed that the predominant Mechanism of competition adsorption between such ions and the counterion in the Represents eluant on the surface of the stationary phase in column 13. For example, there are alkyl chains enter this competition with increasing length in the ions. This leads to an unacceptably long delay and to a bad resolution. This problem can be prevented by changing the counterion to a more hydrophilic inorganic ion. Generally it is when the sample of ions is more hydrophobic, it is preferred to use counterions which are less hydrophobic in order to prevent the chromatographic To optimize separation of ions. For example, the ammonium ion can be used as a counterion for

the analysis of anionic plasticizers are used, while the perchlorination Sls counterion for separations cationic surfactants can be used. The barrier pillar is more fundamental Significance to reduce the background conductivity of the counterion.

When analyzing such strongly hydrophobic ions, the ion-pair mechanism probably predominates. In this case, the counterion and the ions do not form reversible ion exchange sites, but rather reversible ones ion pairs, which in turn form reversible adsorption bonds with the chromatographic bed for different purposes Delay the ions form on the bed. It is believed that this is an essential Factor is in the chromatographic separation.

It is emphasized that the choice of counter-ions significantly affects the degree of adsorption of the ion pairs influenced on the stationary phase. The more organic a counterion is, i. H. the longer the coal changed can be.

The eluant can be specified for the entire process. The alternative is the system especially adapted to the use of continuously changing concentrations of the reagents, aiso to an arrangement commonly referred to as a gradient system. In the alternative x can be gradual Changes in concentration are also used

Another feature of the invention is stability of the organic resin described. It is suitable for long-term use without being destroyed the analysis of anions. The Co ions for the anion analysis can also be strong anions, such as hydroxide, which can easily be suppressed in a blocking column, which is useful for determining the conductivity of Meaning is. This is in contrast to the typical Co ions, which are found in fillings with a bonded phase occur and which cannot be suppressed.

25th

ienstofikcttc is in the molecule, the more solid it becomes Counterion held and thus the ion pair. Thus, it is beneficial for inorganic ions to be highly organic To use counterion compounds, e.g. B. Compounds with 1 to 20 carbon atoms in the Chain. The reverse is true, as will be described below, for strongly organic ions such as surface-active ions Substances, preferably to use inorganic compounds as counter-ions, in order to prevent excessive delay times.

The process steps to be carried out after the separation according to the ion pair theory are the same as those described above with reference to the theory of reversible ion exchange became. This means that after the chromatographic separation, the eluent passes through the barrier column 14 and then through the conductivity cell 15 for measurement by means of a conductivity meter 16 and for a visible printout on the registration device 17.

It is a particular advance of the invention, a technique for analyzing anionic surfactants To make materials available. While the techniques of infrared spectroscopy and nuclear magnetic Providing some information regarding anionic surfactants, they are resonance but of limited value in determining size and molecular weight distribution. Also is ion chromatography is unable to analyze organic surface-active substances.

Another advantage of the invention is the discovery that ion pair chromatography (or reversible Ion exchange chromatography) can be used effectively for inorganic anions or cations can.

A significant advantage of the system described, which affects the whole area (both in the method of the reversible ion exchange as well as with the method of paired ions) is the ability, the capacity (Number of counterions adsorbed on the surface of the column) and the selectivity (relative delay of ions retained on the column by such counterions) by varying the concentration and type of counterion, developing reagent and polar organic liquid in order to adapt the sample type to be analyzed. The system is so flexible that the same stationary phase for separation for analysis of cations or anions around

example 1

This example describes the separation of several inorganic anions using a packing made of a porous chromatographic organic resin. A 4 mm by 250 mm column of stainless steel, which had been charged with a porous resin similar to the resin XAD-2 Amberlite, but with a surface area of 400 m ² / g, was equilibrated with an eluent consisting of 0.002 M Tetrabutylammonium hydroxide and 0.002 M sodium carbonate dissolved in 15/85 (v / v) acetonitrile / water. The flow velocity

speed was 1.5 ml / min. After equilibration, the effluent from this column was passed onto a 4 mm χ 250 mm column with a cation exchange resin, which is sold under the trademark Dowex50WX-16, in the hydrogen form and then into a conductivity detector from Dionex Corp. introduced. There were 100 μΐ a solution containing 3 ppm F, 4 ppm Cl-, 10 ppm NO2 "" 50 ppm PO4 ^3, 10 ppm Br-, NO3- 30 ppm and 50 ppm SO4- contained injected. FIG. 2 shows that a1, ¹ ": seven anions can be separated in less than 12 minutes.

Example 2

This example describes the separation of inorganic sulfate and organic anionic surfactants Fabrics. A 4mm by 250mm stainless steel column was attached to another Approach of the resin according to Example 1 charged The column was at a flow rate of 0.5 ml / min equilibrated with an eluent of 0.01 M ammonium hydroxide in 38/62 (v / v) acetonitrile / water. After equilibration, the effluent from the column was transferred to a 4 mm χ 100 mm column of a cation exchange resin, in the form of a sulfonated resin (diameter ± 1 μ) in the hydrogen form, such as it from Dionex Corp. under the trademark DC 6 A, and then to a conductivity detector directed. A solution which

Contained 35 ppm linear alkylbenzenesulfonates (LAS) with an alkyl chain length of 9 to 14 carbon atoms, was passed through an equilibrated column. The chromatogram in FIG. 3 clearly shows that the sample

13 14

Contained at least 10 components

Example 3

This example shows the separation of organic s
Cations. A pumped stream of 5 mM hexanesulfonic acid was pumped at a flow rate of
3.0 ml / min on a 4 × 250 mm column of porous resin, as described in Example 1, passed 10

The effluent from this column was passed to an anion exchange column, which consists of a
3 χ 250 mm Dowex-1-XlO column in hydroxide ion form and was subsequently led into a LJ.'tä.- ability cell. Fig. 4 shows the results, di> is
were obtained when 20 μΐ of a solution containing 25 mg / l

each of NH ₄ ⁺ , HOCH ₂ CH ₂ NH ₃ * and (CHa) ₃ NH- *

was injected into the column. " I.

Example 4 20 |

This example shows the use of a single |

Column for the separation of anions or cations by Ii

^f simple change of the eluent. An egg

a 4 χ 250 mm column, which is covered with the porous resin according to 25 f

Example 1 was filled as described in Example 3 |

ben to separate a mixture of 15 mg / 1 from f

jeveiis NH ₄ ". CH ₃ NH ₃ ^, HOCH ₂ CH ₂ NH ₃ ⁺ , 1

(CH ₃ ) ₃ NH ₂ * and (CH ₃ J ₃ NH ⁺ inserted The result- |

These are shown in FIG. 5 shown 30 |

This column was then pumped with a |

Stream of water washed until the pH of the |

Discharge was neutral. Then the column was marked with |

a pumped stream of 1 g / l tetrabutylammoni- I

Umhydroxid in water with a flow rate of 35 j

Treated νοη 2 ml / min. It was about 1 1 by the I.

Pumped column. J

Then a pumped stream with a flowing s

speed of 0.7 ml / min of 1 mM Tetrabuty-2

ammonium hydroxide and 5% (v / v) acetonitrile on the 40 "J

Column, which was previously treated with tetrabutylammonium- '{

bromide as described above. |

The effluent from the column with porous resin was adjusted to I.

a stripping column given in the form of a 6 250 mm I.

large Dowex 50W XI6 column in the hydrogen ^ - 45 |

form and was subsequently included in the conductivity \

cell directed 20 microliters of a mixture | from 4 mg / 1 F-, 5 mg / ϊ Cl-. 10 mg / ", NO ₂ -, 20 mg / 1 Br-
and 30 mg / 1 NO ₃ - injected. The results are in

Fig. 6 shows an excellent 50 t

Resolution of the anions h through the above for separation

tion of cations used column. I.

For this purpose 3 sheets of drawings

55

Claims (1)

Patent claims: 1. Process for the separation of anions or cations in a polar mobile liquid phase, characterized in that a) the eluant as a polar mobile liquid phase containing an ion exchange point forming compound through a first column with a porous, hydrophobic chromatographic Bed with essentially no permanently adhered ion exchange sites is, the ion exchange site forming compound a counterion with one of the Ions of opposite charge and also a co-ion with a charge equal to the ions includes, b) the eluant from the first column through a za-tite column with an exchange resin from a Tvps. which essentially excludes the passage of counter ions and Co ions in ionic form.